Carburettors for internal combustion engines



1956 c. R. B. SMITH ErAL 2,756,033

CARBUREJTTORS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 8, 1954 4Sheets-Sheet 1 llllllll ll .F'nankJfp BY July 24, 1956 c. R. B. SMITH L2,756,033

CARBURETTORS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 8, 1954 4Sheets-Sheet. 2

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July 24, 1956 c. R. B. SMITH EI'AL CARBURETTORS FOR INTERNAL COMBUSTIONENGINES Filed Nov. 8, 1954 4 Sheets-Sheet 4 IN VEN T0 Ra: (Zyzyc'ZRevjlleflpllang 77w Izon,

ATTORNEYS.

FIG. 5

United States Patent CARBURETTORS FOR INTERNAL COMBUSTION ENGINES CyrilReville Bellamy Smith, Sutton Coldfield, and Frank Henry Thomas Izon,Birmingham, England, assignors to Amal Limited, Witton, Birmingham,England, a corporation of Great Britain Application November 8, 1954,Serial No. 467,475

Claims priority, application Great Britain November 19, 1953 3 Claims.(Cl. 261-44),

This invention relates to carburettors for internal combustion engines,particularly those employed in association with motor cycles.

It is an object of this invention to provide an improved carburettor foran internal combustion engine.

According to this invention a carburettor for an internal combustionengine comprises in combination a main body portion, a float chamber forfuel, a float in the float chamber, a fuel-cut-oif device associatedwith said float to control the admission of fuel into the float chamberin accordance with the volume of fuel in the float chamber, a passageformed through said main body portion, said passage forming an airintakepassage, a chamber in which air and fuel may be mixed and a mixtureoutlet passage, a pistontype throttle adapted to control the amount ofair passing along the air-intake passage, a needle jet indirectlyconnected to the float chamber and in communication with the mixingchamber, a metering needle movable with the piston-type throttle valveand adapted to co-operate with the needle jet to control the amount offuel entering the mixing chamber in accordance with the amount of airpassing along the air-intake passage, a primary air-intake passageseparate from, and uninfluenced by any turbulence in, the air-intakepassage, said primary air-intake passage communicating with an annularspace around said needle jet, a pilot fuel passage discharging into themixture outlet passage, a pilot air supply associated with the pilotfuel passage, and a bleed hole in the needle jet communicating with theannular space around said needle jet.

According to one feature of the invention, at least one wall of thefloat chamber is formed by part of the main body portion.

According to another feature of the invention, the float ispivotally-mounted in the float chamber.

A carburettor in accordance with an embodiment of the invention is shownin the accompanying drawings of which:

Figure l is an elevational view'of the carburettor;

Figure 2 is a sectional view of the carburettor taken along the lineII--II of Figure 1;

Figure 3 is a sectional view of the float chamber, taken along the lineIIIIII of Figure 1;

Figure 4 is a sectional view taken along the line IV--IV of Figure 2;and

Figure 5 is a sectional view taken along the line V-V of Figure 2.

Referring to the drawings, the carburettor comprises a main body portion1, generally of cruciform cross-section. This body portion has a maintransverse bore which provides an air-intake passage 3, and a mixtureoutlet passage 5. The air-intake passage 3 is bored eccentrically in thepart 7 of the main body portion which has screwed to it a funnel 9. Theopen end-portion of the mixture outlet passage 5 is provided with aflange 11 which will be utilised for attaching the carburettor to anassociated internal combustion engine (not shown).

A cup-shaped member 13 co-operates with part of the 2,756,033 PatentedJuly 24, 1956 main body portion in a fluid tight manner so as to form afloat chamber and an aperture 15 in that part of the main body portionallows access of fuel from the float chamber to the interior of the mainbody portion as will be described later.

The cup-shaped member 13 (see particularly Figure 3) is provided with anintegral upstanding substantially cylindrical hollow boss 17 into whichis threaded a hollow plug 19 generally of cruciform cross-section. Afibre gasket 21 is provided between the boss and the plug 19 in order toprevent any leakage of fuel. A connecting plug 23 (which will be securedto a source of fuel) is slipped over the upper end portion of the hollowplug 19 and is secured to it by a screw 25 which is threaded into theupper end portion of the hollow plug 19. Gaskets 27 and 29 preventleakage of the fuel between the several parts. A cylindrical chamber 31is provided between the upper end portion of the hollow plug 19 and theconnecting plug 23, and a diametral bore 33 connects the cylindricalchamber 31 with the interior of the hollow plug 19. The interior of thehollow plug 19 has a shouldered portion 35 with which a needle-type fuelsupply valve 37, triangular in cross-section, co-operates. guided formovement by the hollow plug and passes into the cup-shaped member 13 andits end is supported upon one arm 39 of a lever. The lever ispivotally-mounted upon a pin 41 secured to the internal Wall of thecupshaped member 13 and the other arm 43 of the lever is secured to'acylindrical float 45. A substantially-cylindrical wire gauze filter 47is disposed in the chamber 31.

A second integral upstanding substantially-cylindrical boss 49 on thecup-shaped member 13 is internallythreaded and co-operates with a sleeve51. is resiliently mounted in the sleeve 51 by a spring 55 and a bore 57in the tickler acts as an air vent for the float chamber.

The cup-shaped member carrying its associated parts is attached to thehollow boss 59 formed on the main body portion by screws 61 (see Figurel) and a circular wire gauze filter (not shown) is disposed within theboss and abuts against the shoulder 63.

The lower part 65 of the main body portion has an inwardly-directedportion 67 and a cylindrical 'jet block 69 is disposed within the mainbody portion, resting upon the inwardly-directed portion, and is securedin position by a set screw 71 (see Figure 4). The jet block 69 has asubstantially-cylindrical bore 73 which is aligned with p the air-intakepassage and the mixture outlet passage and which forms a mixing chamber.A hollow plug 75 is threaded into the lower portion of the jet block 69and this hollow plug has threaded into its upper end portion a needlejet 77 and into its lower end portion a main jet 79. The hollow plugco-operates with a fibre washer 81 to form a fluid-tight joint with thebottom of the main body portion (as shown in Figures 2 and 5). A closurewell member 83 is threaded into the lower end portion of the hollow plug75 so as to seal the bottom of the hollow plug 75.

A fuel-receiving chamber 85 is formed between the hollow plug 75 and thelower part 65 of the main body portion and communicates with theaperture 15. In-

clined holes 87 in the hollow plug 75 connect the fuelreceiving chamber85 with the closure well member 83 and hence indirectly with the mainjet 79 and the needle one not designated, bored in the main body portionand .in the jet block 69 respectively, are associated with the Theneedle-type valve 37 is v A tickler 53 Pilt i k u p am unt at Pfi 3 I9 1i pilot fuel jet 89i's Controllable by pilot fuel jet 109 and a screw101 threaded into a sleeve 193 which, in turn, is aded in a h a he qrrart fi he main-b s ns portion is provided for reaming the pilottu el-jA supplyof pilot air (see FigureA) is suppl ed -to-the passage95, formixing with the supply ot pilct'iuelby way of passages 105, 107, 109,and 111 bored;-injthe lower part of the main body portion andinflhe jet;block 69 The amount of pilot air supplied is -contro l 1 .10 lable, by apilotair control screw 113 which ist'hreaded W into a hole in the lowerpart 65 of the main body portion, therebeinga coiled spring 115 disposedhetweenthe head; of es w and h ma o r tiq ff pas a ew mcnqesin t t P t 70 the ma qdy po ion-w ,15 is not bored eccentrical ly and so;lSJll'lll'lllUdlTlQfllbY any turbulence which may occur-inthe,ahtintalge passage 3.,

Primary air is supplied to the mixing chamber side of; the metering tube(see Figures land 4) by Way of passage 117 bored in that part 7 of themain body portion 20 which isnot bored eccentrically, and passage 119which is bored in the jet block 69 and which communicates with anannular space around the needle jet. A primary air jet tube 121 isprovided in the passage 117,'its internal diameter determining theamount of primaryair passing. 2 Since the passage 117 commences in thatpart 7 of the main body portion which is not bored eccentrically, thesupply of primary air is not influenced by turbulence in i theair-intake passage 3.

A bleed hole 123 in the needle jet 77, communicating with the annularspace around the needle jet allows fuel 1 to be, mixed with the primaryair to be available for rapid acceleration. The bleed hole is arrangedtobe slightly below the mean level of the fuel, e. g. of an inch, andslightly above, e. gJA of an inch, the calibrated orifice of the needlejet.

A piston-type throttle sleeve 125 of orthodox form is; pqssd t e up P rQt h ma abqd P0 tion and co-operates with the mixing chamber todeterminethe amount of air passing from the air-intakepas- 40 sageStothe mixture outlet passage 5. The pistontype throttle sleeve iscontrolled by means ofa Bowden wire 127 which passes through a sleeve129 threaded in acap 131 to the outside of the carburettor, A spring 133is disposed between the cap 131 and the upperparoofthe throttlesleeve.

A ra l me ber 135 o do f rm. sa pq a ed with the throttle sleeve and isoperable againstthe action v of spi n 1. 5 dmw m wh h-pa e ugh a sl e e1 ea d-in t e an .131- yli der. A F PQ ..%1 I Pa f the sp 1137 v. s;t s=stranglen member durin g its movement,

A m t r aanes e 45 d e o 15mm w t the ia in to n l he ma n amount fs s spp ied; to the mixing chamberis fastened to the head of the thrpt Q tlesleeve by. a bifurcatedspringplip 147 which engages with one pf a-seriesof grooves formed at the upperend a,

portion pf the needle.

The cap 131 is secured to the upper part of the main; bodypor-tion by alocking ring 14? which is threadedon to the outer surface of the mainbody portion. A spring clip 151 secured by a-screw 153 to the cap.ptevents undesired; rotation of the locking ing. u q

A throttle stop 155 is threaded into the body portion (see Figured) andits upper end determines the location of the throttlesleevewhen in itsclosed position Move ment ot the throttle stop due tovibration is;prevented by; a coiled spring 157 disposed between the head of thethrottle sto a e a nrho P on.

It appears that by providingthebleedhole 12 3, a small well of f ue l isalways available inthe annular space around the sgdl ti t for s a emigtion; W t is wal et fuel ha bcc w ss n n w nah re on ied ,-.th

consequent leyel drop whichtalgeaplace allows aintq'pass usbthe b e 91 wt a.consequsa twe n nstot,

the mixture at mid-throttle positions. This weakening at themid-throttle positions leads to an increased performance.

In a modified form of the carburettor just described.

a hollow boss cast inone with the main body portion co; operates with acover plate to provide the float chamber.

For instance with a motor cycle having a 650 cc. engine,

working-under identical conditions. the followingzresults u With a motorcycle having a 250 cc. engine, tworking under identical conditions, thefollowing resultswere ob:

tained:

Old type Carburottor carburettor in accordance Speed, miles per hourmiles pet with lnven gallon tion, miles, per gallon Consequentlythere-is a 15-20% reductionin fuel consumption with superioracceleration properties.-

We claim:v

1. A carburettor for an internal combustion engine comprisingdncombination a main body portion, a-fioat chamber for fuel, a float insaid float chamber, a fuel cut-ofl device associated with said float tocontrol the admission .of fuel into said float chamber in accordance:with the volume of fuel containedtherein, a passage:

formed through said main bodyportion said passageforming an air-intakepassage, achamber in which air and fuel may be mixed and a mixtureoutlet passage,--a

piston-type throttle adapted to control the amount of air passing alongthe air-intake passage, a needle jet indirectly t connected to the floatchamber and in communication with the mixingchamber, a metering needlemovable with the piston-typethrottle valve and adapted to cooperate'withl said needle jet to control the amount of fuel entering-the intakepassage communicating with an annular space around said needle'jet, apilot fuel passage discharging i into the mixture outlet passage,a'pilot air supply 3.580% ciated with the pilot fuel passage,- and ableed hole in said 1 needle jet=communicating with theannularspacearound said needle jet, said bleed hole being disposedslightlyi' belowthe mean level ofthe fuel and slightlyabove thecalibrated orifice of the needle jet.

2. The structure defined in claim l wherein at least one i wall of thefloat chamber is formed by part of the mainbody portion.

3. The structure defined in claim .1 wherein said fioat is pivotallymountedin said float'chamben Referencestfilited in the file of thispatent FOREIGN PATENTS mixing chamber in accordance with the amount, ofair passing along the air-intake passage,-a primary -air-intakepassageseparate from, and uninfluenced by any turbulence r in said firstmentioned air-intake passage, said primaryain l

